Composite vane and method of manufacture

ABSTRACT

A vane having a profile capable of formation by pultrusion is disclosed. The vane can be used for removing liquids entrained in a gas stream. The vane includes a main curved section oriented generally parallel to the gas stream and curved to reorient the gas stream, the main curved section causing a first and a second change of direction of the gas stream; a first air pocket formed on a first side of the main curved section, the first air pocket sized and oriented into the gas stream where the gas stream first changes direction; and a second air pocket formed on a second side of the main curved section, the second air pocket smaller than the first air pocket and sized and oriented into the gas stream where the gas stream makes the second direction change.

BACKGROUND

Virtually all air intake systems require an air filtering mechanism tomaintain inlet air free of contaminants. This requirement isparticularly true of shipboard engines and ventilation systems thatoperate in a salt spray environment, where moisture and salt particlesimpinging, for example, on fast spinning turbine blades can cause severedamage to the ship's propulsion system. In this environment, thefiltering mechanism must be able to separate moisture from the inletair, providing dry and clean air to the ship's propulsion system orventilation system. This requirement is equally important in trains,offshore platforms, and other wet environments, among otherapplications.

In a specific example of a shipboard application, most naval vesselsrely on fossil fuel for propulsion, and many of these vessels arepowered by gas turbines. Gas turbine engines require significantquantities of air for combustion. This air is drawn into the combustionchamber through an air intake. The air intake, ideally, would be as highas possible above the waterline to minimize the possibility of waterentrainment (i.e., entrainment of ocean spray) in the intake air stream.Because the air intakes are located high on the ship, their weightshould be minimized to avoid making the ship less stable and moresusceptible to rolling, and in a worst case scenario, capsizing.

SUMMARY

What is disclosed is a composite vane, having a profile capable offormation by pultrusion, for removing liquids entrained in a gas stream.The composite vane has a main curved section oriented generally parallelto the gas stream and curved to reorient the gas stream. The main curvedsection causes a first and a second change of direction of the gasstream. The composite vane also includes a first air pocket formed on afirst side of the main curved section, the first air pocket sized andoriented into the gas stream where the gas stream first changesdirection, and a second air pocket formed on a second side of the maincurved section. The second air pocket is smaller than the first airpocket and sized and oriented into the gas stream where the gas streammakes the second direction change.

DESCRIPTION OF THE DRAWINGS

The Detailed Description will refer to the following drawings in whichlike reference numbers refer to like items, and in which;

FIG. 1 illustrates, in horizontal cross section, exemplary compositevanes for use in a moisture removal application;

FIG. 2 illustrates a typical application of the composite vanes of FIG.1; and

FIGS. 3A and 3B are graphs showing measured pressure drop and dropletremoval efficiency for the composite vanes of FIG. 1.

DETAILED DESCRIPTION

A composite vane as shown in the above figures, and as described belowcan be used in air intake systems such as naval applications related topropulsion system air intakes to maximize liquid droplet removalefficiency while addressing design tradeoffs related to ship stabilityand system maintenance.

While the discussion that follows will focus on the shipboard and navalapplication of this technology, those skilled in the art will understandthat the claimed invention can be applied in many other fields ofendeavor, including non-shipboard moisture separation applications. Inparticular, the composite nature of the air intake vane makes it idealwhere corrosion resistance is important, where reduced weight isimportant, and where rigidity and strength are important. In addition,the herein described composite vane is inexpensive to form, compared toprior art moisture separators, is not subject to stress cracking as inprior art systems, and requires no maintenance.

Ship stability (resistance to roll) can be defined in terms of theship's center of buoyancy B, center of gravity G, and metacenter M. Whena ship is exactly upright, these three “centers” are aligned vertically.When a ship tilts (rolls to port or starboard) the center of buoyancy Bof the ship moves laterally. The point at which a vertical line throughthe tilted center of buoyancy crosses the line through the original,non-tilted center of buoyancy B is the metacenter M.

The distance between the center of gravity and the metacenter is calledthe metacentric height, and is usually between one and two meters. Thisdistance is also abbreviated as GM. As the ship heels over (rolls byangle φ), the center of gravity G generally remains fixed with respectto the ship because the center of gravity G just depends upon positionof the ship's mass and cargo, but the M, moves up and sideways in theopposite direction in which the ship has rolled and is no longerdirectly over the center of gravity G.

The righting force on the ship is then caused by gravity pulling down onthe hull, effectively acting on its center of gravity G, and thebuoyancy pushing the hull upwards; effectively acting along the verticalline passing through the center of buoyancy B and the metacenter M aboveit. This creates a torque that rotates the hull upright again and isproportional to the horizontal distance between the center of gravity Gand the metacenter M (i.e., the metacentric height). The metacentricheight is important because the righting force is proportional to themetacentric height times the sine of the angle of heel. Moreover, if themetacentric height approaches a small value, any rolling of the ship cancause the metacenter M to be displace below the center of gravity. Inthis condition, the ship will capsize. Accordingly, ship designersalways are concerned about adding weight to a ship above its waterlinebecause such added weight decreases the metacentric height and leads toa less stable ship.

Any air intake system intended for shipboard applications should bedesigned to facilitate preventive maintenance, and in particular toaddress possible corrosion concerns. By using a composite vane asopposed to more traditional stainless steel or aluminum vanes, manypreventive maintenance problems can be avoided.

The disclosed composite vane falls into the class of inertial impactionseparators. Inertial impact separation occurs when a gas passes througha tortuous path around vane pockets while the solid or liquid dropletstend to go in straighter paths, impacting these pockets. Once thisoccurs, the droplet coalesces within the vane pockets and drains awayfrom the air. The composite vane weighs much less than comparablestainless steel vanes, and thus leads to a more stable ship design.

To form such a composite vane, a manufacturing technique know aspultrusion may be used. Pultrusion (pull+extrusion) is particularlywell-suited for the formation of products from composite materials. Thepultrusion process begins when racks or creels holding rolls of fibermatt or doffs of fiber roving are de-spooled and guided through a resinbath or resin impregnation system. The fiber may be reinforced withfiber glass, carbon, aromatic polyamide (aramid), or a mixture of thesesubstances. In some pultrusion processes, the resin may be injecteddirectly into a die containing the fiber.

The resin used in pultrusion processes is usually a thermosetting resin,and can be combined with fillers, catalysts, and pigments. The fiberreinforcement becomes fully impregnated with the resin such that all thefiber filaments are thoroughly saturated with the resin mixture. Thethermosetting resin may be selected from the group consisting of vinylester resins, epoxy resins, and combinations thereof.

As the resin-saturated fiber exits the resin impregnation system, theun-cured composite material is guided through a series of tooling thathelps arrange and organize the fiber into the desired shape while excessresin is squeezed out (debulked). Continuous strand mat and surfaceveils may be added in this step to increase structure and surfacefinish.

Once the resin impregnated fibers are organized and debulked, theun-cured composite passes through a heated die. The die is typicallymade of steel, may be chromed (to reduce friction), and is kept at aconstant temperature to cure the thermosetting resin. The material thatexits the die is a cured, pultruded fiber reinforced polymer (FRP)composite.

A surface veil may be applied to the FRP composite. Such a veil may, forexample, be used to adjust (increase or decrease) surface wettability.

The composite material is then cut to the desired length by a cut offsaw, and is ready for installation.

One goal that must be achieved in designing a composite vane, andincorporating these composite vanes into a coalescer, is to maximizeliquid droplet removal efficiency while preventing liquidre-entrainment. Re-entrainment occurs when liquid droplets accumulatedon the vanes are carried off by the exiting gas. This occurs when theforce exerted on the liquid droplets clinging to the vanes due to thevelocity of the exiting gas, or annular velocity, exceeds thegravitational forces of the draining droplets (see FIG. 2). Thus, indesigning a composite vane (and its corresponding coalescer), thefollowing parameters may be taken into account: gas velocity through thecoalescer stages, annular velocity of gas exiting the stages, solid andliquid aerosol concentration in the inlet gas, and drainability of thecoalescer. Each of these factors with the exception of the inlet aerosolconcentration can be controlled. At a constant gas flow rate, gasvelocity can be controlled by either changing the profile and spacing ofthe vanes or by increasing or decreasing the number of vanes used.

At a constant gas flow rate, the exit velocity of the gas can becontrolled by changing the spacing between the vanes. Drainage can beimproved by either selecting low surface energy vane materials or bytreating the vanes with a chemical or applying a material that lowersthe surface energy of the vane material to a value lower than thesurface tension of the liquid to be coalesced. Having a low surfaceenergy material prevents liquid from wetting the vane material andaccelerates drainage of liquids down along the vanes. The liquidcoalesced on the vanes falls rapidly through the network of vaneswithout accumulating on the vanes where it could be re-entrained.

FIG. 1 shows a profile of exemplary composite vanes 100 for use in anair intake application to remove moisture from combustion or ventilationair. Use of a FRP composite reduces weight, increases corrosionresistance, and reduces maintenance compared to the same vane profileformed using aluminum or stainless steel. The vanes have a width ofabout 5 inches, a height of about 1.75 inches, and as installed, aseparation of about 1 5/16 inches at the inlet 104 and outlet 106, whichare formed by arranging two of the composite vanes 100 in parallel asshown. However, vane separation may be varied, for example to as much asapproximately 1.875 inches or more. The separation between the vanes 100narrows in the regions containing pockets 120 and 130. In these regions,the separation may be about 0.75 inches. Vane thickness varies fromabout 3/16 inch to ⅛ inch, as shown. The thickness of the compositevanes 100 is determined based on considerations of rigidity in use, easeof formation by pultrusion, and minimal weight. The combination of theseconsiderations results in the thicknesses shown in FIG. 1. The vanes 100may be any length, and typically are about 5 inches to about 144 incheslong. Air passage past the vanes 100 is indicated by the arrow 101.

Each vane 100 comprises a main curved section 110 and the two airpockets 120 and 130. The volumes of the air pockets 120 and 130 arechosen to maximize removal of liquids from the liquid-gas mixture. Theair pockets 120 and 130 extend over the entire length of the vane 100.Although the main curved section 110 is shown as a series of flats, themain curved section 110 may, alternatively, comprise a smooth curvehaving approximately the same general shape as that of the series offlats illustrated. Because the air is made to change directions rapidlywhen moving past the curved sections 110 of the vanes 100, moistureentrained in the air can be removed easily. More specifically, at eachchange in direction caused by the shape of the composite vanes 100, acentrifugal force is exerted on the liquid-gas mixture, which throws therelatively heavy liquid droplets against the wetted vane walls. Theliquid droplets coalesce into larger particles, absorb other particles,coalesce into sheet flow, and drain to a liquid sump at the bottom ofthe composite vanes 100 (see FIG. 2). In addition, liquid-gas mixturestraversing the composite vanes 100 in the direction of the arrow 101travel toward the pockets 120 and 130, where coarse droplets arecaptured by the first pocket 120 and smaller droplets are captured bythe second pocket 130 after acceleration through the venturi throatcreated by the first pocket 120. The air pockets 120 and 130 alsofurther convolute and agitate the air stream, causing additionalmoisture separation. Once the liquid enters the pockets 120, 130, theliquid is isolated from the gas stream and drains by gravity into theliquid sump. Similar to moisture separation, solid particles may beremoved from the liquid-gas stream due to the abrupt changes indirection of the gas as it passes through the composite vanes 100.

The relationship of the composite vanes 100 shown in FIG. 1 allows anincrease in the speed of the gas flowing through the vanes 100 withoutre-entrainment of separated fluids. Furthermore, the narrowing of theseparation between composite vanes 100 that occurs in the regionscontaining the pockets 120 and 130 creates throats 108. These throats108 cause the liquid-gas mixture to accelerate, which makes removal ofliquid droplets more efficient. Subsequent to flow through the throats108, the liquid-gas mixture is expanded, and slows, so that the velocityof the mixture at the outlet 106 is the same as that at the inlet 104.With such construction, the vanes 100 can provide up to 90 percentremoval efficiency for liquid droplets as small as 20 microns indiameter and 100 percent removal efficiency for 30 micron-diameterdroplets.

FIG. 2 illustrates a typical application of the composite vanes ofFIG. 1. As shown in FIG. 2, a shipboard air inlet plenum 200 ispopulated with a series of the composite vanes 100. Each vane 100 may beformed separately by the pultrusion process. Moisture entrained in theinlet air is removed at an efficiency of as much as 100 percent bypassage past the vanes 100. The collected moisture drops by gravity tothe bottom of the plenum 200, and may be removed. In a shipboardapplication, by using lightweight vanes made of a FRP composite, theship's metacentric height is maximized.

FIGS. 3A and 3B are graphs showing measured pressure drop (DP) anddroplet removal efficiency (percentage removed), respectively, for acomposite vane and different airflows. The curves illustrated are for avane similar in profile to that shown in FIG. 1, with multiple vanesspaced about 1 5/16 inches apart. The measured results show that thecomposite vanes 100 perform at least as well as comparably-shaped vanesmade, for example, of extruded aluminum. The results shown in FIGS. 3Aand 3B correspond closely to experimental results obtained usingcomputational fluid dynamics (CFD) to model the airflow. With this CFDmodel, a two-dimensional grid of triangular cells is used for the vanemodel. The CFD program is FLUEN™ Version 6.2, which uses theNavier-Stokes equations with K-ε model of turbulence.

Although disclosed applications of the vane 100 include shipboardinstallation into a gas turbine air inlet system and a ventilationsystem, the vane 100 has many other applications, including for othertypes of marine propulsion systems. In addition, the vane 100 may beused to remove condensate from vapors and absorptive liquid from treatedgases. In an embodiment of the composite vane 100, a surface veil and anintermediate veil can be applied. Such a surface veil may reduce radarreflectivity. Other surface veils may, as noted above, be used to adjustsurface wettability.

1-19. (canceled)
 20. A method for manufacturing a composite vane for usein removing liquid droplets from a gas stream, comprising: reinforcing afiber material with one or more of fiberglass, carbon and aromaticpolyamide; pulling the impregnated reinforced fiber material through adie; and simultaneous with the pulling step, applying heat at a constanttemperature to the material, whereby the composite vane having a desiredprofile is formed, and whereby the desired profile comprises: a maincurved section oriented generally parallel to the gas stream and curvedto reorient the gas stream, the main curved section capable of causing afirst and a second change of direction of the gas stream; a first airpocket formed on a first side of the main curved section, the first airpocket located on the composite vane where the gas stream first changesdirection; and a second air pocket formed on a second side of the maincurved section, the second air pocket smaller than the first air pocketand located on the composite vane where the gas stream makes the seconddirection change.
 21. The method of claim 20 further comprisingimpregnating the reinforced fiber material with a thermosetting resin.22. The method of claim 21, wherein the impregnating fully impregnatesthe fiber material with the thermosetting resin such that all the fiberfilaments are thoroughly saturated with the resin mixture.
 23. Themethod of claim 21 wherein the thermosetting resin is combined withfillers, catalysts, and pigments.
 23. The method of claim 21 wherein thethermosetting resin is selected from a group consisting of one or moreof vinyl ester resin and epoxy resins
 24. The method of claim 20 furthercomprising applying a surface veil to the composite vane to adjustsurface wettability.
 25. The method of claim 20 further comprisingapplying additional layers to the composite vane, wherein the layersoperate to reduce visibility to radar
 26. The method of claim 20 whereinthe main curved section is formed with a smooth curve.
 27. The method ofclaim 20 wherein the main curved section is formed with a series offlats approximating a smooth curve.
 28. The method of claim 20 whereinthe main curved section is formed with a thickness of about 3/16 inchand the first and the second pockets are defined by pocket walls havingthicknesses of about ⅛ inch.
 29. The method of claim 20 wherein thecomposite vane is formed with a width of about 5 inches and a length ofbetween about 5 inches and about 144 inches.
 30. The method of claim 20further comprising: repeating the reinforcing, pulling and simultaneousapplying heat steps to form a plurality of composite vanes; and placingthe plurality of composite vanes at a predetermined separation to removethe liquids from a gas stream.
 31. The method of claim 30 wherein theplacing places the plurality of composite vanes in a plenum housing theplurality of composite vanes.
 32. The method of claim 31 furthercomprising coupling a coalescer to an exit from the plenum, thecoalescer comprising a filter material to further remove the liquiddroplets.